1. Field of the Invention
The present invention is generally in the field of fabrication of semiconductor structures and circuits. More particularly, the invention is in the field of fabrication of semiconductor on insulator (SOI) structures and circuits.
2. Background Art
Semiconductor structures such as transistors and isolating trenches are conventionally fabricated on several types of silicon wafers. For example, such structures can be fabricated on bulk silicon wafers or silicon on insulator wafers. Bulk silicon wafers typically have a substantially uniform composition, while semiconductor on insulator wafers typically have a layered composition. Once fabricated on a particular silicon wafer, such semiconductor structures are typically used in a wide variety of circuits, including switching circuits.
Each type of silicon wafer utilized for fabricating such semiconductor structures suffers from attendant drawbacks. For example, it is difficult to electrically isolate semiconductor structures fabricated on a conventional bulk silicon wafer, because although such semiconductor structures can be partially electrically isolated by virtue of, for example, their isolating trenches, electric current can still flow under such trenches, leading to, for example, voltage and current fluctuations. Neighboring semiconductor devices, e.g. neighboring cascaded transistors, in such structures thus tend to interfere with one another when fabricated on bulk silicon wafers. In contrast, it is easier to electrically isolate semiconductor structures or circuits implemented on a conventional silicon on insulator wafer, in which a buried oxide layer provides additional isolation. Unfortunately, circuits designed for fabrication in a bulk silicon wafer must be redesigned for fabrication in a conventional silicon on insulator wafer, which significantly increases manufacturing and integration complexity and cost.
Thus, there is a need in the art for semiconductor structures and circuits that overcome disadvantages associated with utilizing conventional bulk silicon and silicon on insulator wafers.